THE 



AMERICANJOURNALOFSCIENCE 



[FOURTH SERIES.] 



Art. I. — A Geologic Reconnaissance of the Cuzco Valley, 



Peru; by Herbert E. Gregory. 1 With Plates I and II. 



Contents. 



Page 



Introduction 2 



Scope of the paper 2 



Note on the topographic map 8 



Note on the geologic map 7 



I. Topography 7 



Topographic setting 7 



Belief . 7 



The three basins 10 



Drainage 10 



Lakes 16 



II. Physiography 17 



Regional relations . 17 



Land forms in Cuzco Valley 19 



Factors conditioning erosion 19 



Mountains 21 



Plateaus 24 



Mature slopes 26 



Valleys 28 



The Huatanay Valley ._ 28 



Contrasted portions of valleys 31 



Relation of valleys to structure 81 



Valleys in unconsolidated deposits 34 



LakeMorkill 34 



Glaciation 39 



Introduction 39 



Glacial features north of the Cuzco Valley axis 41 



Glaciation features south of the Cuzco Valley axis 44 



Glacial gravels 46 



Distribution and character 46 



Post-glacial erosion of gravels 49 



Terraces 51 



III. The Sedimentary Rocks -- 53 



Introduction 53 



The Qquilque Formation -. 55 



1 Geologist, Peruvian Expedition of 1912, under the auspices of Yale 

 University and the National Geographic Society. 



Am. Jour. Sci.— Fourth Series, Vol. XLI, No. 241.— January, 1916. 

 1 



